This invention relates to an apparatus for detecting an engine crankshaft position .theta..sub.pmax at which the cylinder pressure reaches its maximum value.
In order to achieve high engine performance and high fuel economy, the ignition-system spark-timing is controlled in a manner to maintain the crankshaft angular position .theta..sub.pmax at a crankshaft angular position, for example, 15.degree. after the top dead center of the piston, at which the engine produces a maximum torque. During requests for rapid engine warming, the ignition-system spark-timing may be controlled in a manner to maintain the crankshaft angular position .theta..sub.pmax at 25.degree. after the top dead center of the piston.
For the purpose of these ignition-system spark-timing controls, it is the current practice to employ a digital computer which detects the maximum cylinder pressure by comparing a number of cylinder pressure values sampled from a cylinder pressure indication signal produced from a cylinder pressure sensor. Any attempts to increase the accuracy of detection of the engtine crankshaft position .theta..sub.pmax causes a corresponding increase in the frequecy of sampling operation of the cylinder pressure indication signal. This requires an expensive high-speed analog-to-digital converter, resulting in an expensive apparatus. In addition, the conventional apparatus is sensitive to noise which may be superimposed on the cylinder pressure indication signal, causing an error to be introduced in the sampled data used in detecting the maximum cylinder pressure.